Question

如果从多个表中获取列，如何按列分组并按频率排序？例如，我有3个表，Table_A，Table_B，Table_C。它们中的每一个都有一列相同的数据。例如Table_A

col
------
aaa
bbb
aaa
ccc

例如Table_B

aaa
ccc
ddd
bbb

同样是Table_C的类似数据。我希望得到以下结果：

aaa 3
bbb 2
ccc 2
ddd 1

目前，我有这个

select col, count(*) from Table_A UNION select col, count(*) from Table_B UNION select col, count(*) from Table_C group by col order by count(*) desc

但这并没有给我我想要的结果。感谢

Answer 1

select      col
           ,count(*) as cnt

from        (         select col from Table_A
            union all select col from Table_B
            union all select col from Table_C
            ) t

group by    col

order by    cnt desc
           ,col
;

OR

select      col
           ,sum(cnt) as sum_cnt

from        (         select col,count(*) as cnt from Table_A group by col
            union all select col,count(*)        from Table_B group by col
            union all select col,count(*)        from Table_C group by col
            ) 

group by    col

order by    sum_cnt desc
           ,col
;

Answer 2

首先，使用union all，然后进行聚合。正确的语法是：

select col, count(*) as cnt
from (select col from Table_A
      union all
      select col from Table_B
      union all
      select col from Table_C         
     ) abc
group by col 
order by col;

您也可以预先汇总数据，但需要再次汇总：

select col, sum(cnt) as sum_cnt
from (select col, count(*) as cnt from Table_A group by col
      union all
      select col, count(*) from Table_B group by col
      union all
      select col, count(*) from Table_C group by col
     ) abc
group by col
order by col;

Answer 3

每个select都需要自己的group by子句。

选择col，count（）来自Table_A 按组分组联盟选择col，count（）来自Table_B 按组分组联盟选择col，count（*）来自Table_C 按组分组按顺序排列;

如何使用多个表进行分组和排序

3 个答案: